Three years after the infamous BP oil spill off the Gulf Coast, lawmakers are still trying to nail down the effectiveness of past, present and future relief efforts backed by billions of dollars.

Restoration efforts will receive anywhere from $5.4 billion to $21 billion from parties responsible for the spill, depending on the outcome of ongoing civil trials in New Orleans. Of that, a law passed in July 2012 dictates that 30 percent of funds will go to broad ecosystem restoration, 65 percent will be divided among the five Gulf Coast states – Florida, Louisiana, Mississippi, Texas and Alabama – and 5 percent will be invested in scientific purposes, such as research, monitoring and technology.

“Revenue from the spill penalties gives us an opportunity to restore the environmental health of the Gulf without using federal funds,” Sen. Jay Rockefeller, D-W.Va., chairman of the Commerce, Science and Transportation Committee, said Thursday in a prepared statement before a committee hearing on the Gulf Coast restoration.

The Senate committee heard testimony from a panel of state and federal officials about the progress made in restoration so far, as well as what still needs to be done. Most reported positive steps since 2010 in areas such as tourism, fishing and wildlife preservation, though all admitted there is significantly more work to do and will be for a while.

“While some impacts were apparent immediately, we won’t know the full long-term impacts of the spill for some time, as the effects continue to trickle up through the web,” said Eric Draper, executive director of Audubon Florida.

The Restore Act, passed in 2012, ensures that 80 percent of the Clean Water Act penalties assessed against BP and other responsible parties will go to the Gulf Coast Restoration Trust Fund to help affected states and ecosystems rather than into the federal treasury. BP has spent more than $14 billion in clean up operations apart from what it will pay in penalties, and private donors also have contributed significantly to restoration efforts.

Rockefeller, who did not attend the hearing, was critical of efforts so far in a released statement. He said restoration should be further along than it is, calling efforts from state and local governments “adrift.”

“Despite the current availability of billions of dollars in funding for restoration purposes from litigation settlements to date, only a very small amount has been applied on the ground, and there is no overarching plan in place to guide restoration,” he said.

Mississippi and Florida have created advisory bodies for the allocation of federal money within their states, hoping to make the process more efficient and less bureaucratic. Mississippi’s, called GoCoast 2020, already has identified projects that need funding in eight areas. Florida’s, called the Gulf Consortium, is comprised of one county commissioner from each of the state’s 23 Gulf Coast counties.

Sen. Bill Nelson, D-Fla., who led the committee meeting Thursday, repeatedly emphasized that funds needed to be allocated just as the law indicated.

“I want you to convey, and I’ll do likewise, that we expect the intent of the law to be carried out,” Nelson told the panel. “Someone can’t go out on their own and start doing whatever they want.”

The explosion of the Deepwater Horizon oil rig on April 20, 2010, led to the largest oil spill in U.S. history. The blast killed 11 people and resulted in more than 206 million gallons of oil spilling into the Gulf of Mexico for 84 days.